page_title: Photoinhibition
section_title: What is inhibited
hierarchical_section_title: Photoinhibition / What is inhibited
caption_attribution_description: English: PDB 2axt, using pymol
context_page_description: Photoinhibition is light-induced reduction in the photosynthetic capacity of a plant, alga, or cyanobacterium. Photosystem II is more sensitive to light than the rest of the photosynthetic machinery, and most researchers define the term as light-induced damage to PSII. In living organisms, photoinhibited PSII centres are continuously repaired via degradation and synthesis of the D1 protein of the photosynthetic reaction center of PSII. Photoinhibition is also used in a wider sense, as dynamic photoinhibition, to describe all reactions that decrease the efficiency of photosynthesis when plants are exposed to light.
context_section_description: Photoinhibition occurs in all organisms capable of oxygenic photosynthesis, from vascular plants to cyanobacteria. In both plants and cyanobacteria, blue light causes photoinhibition more efficiently than other wavelengths of visible light, and all wavelengths of ultraviolet light are more efficient than wavelengths of visible light. Photoinhibition is a series of reactions that inhibit different activities of PSII, but there is no consensus on what these steps are. The activity of the oxygen-evolving complex of PSII is often found to be lost before the rest of the reaction centre loses activity. However, inhibition of PSII membranes under anaerobic conditions leads primarily to inhibition of electron transfer on the acceptor side of PSII. Ultraviolet light causes inhibition of the oxygen-evolving complex before the rest of PSII becomes inhibited. Photosystem I (PSI) is less susceptible to light-induced damage than PSII, but slow inhibition of this photosystem has been observed. Photoinhibition of PSI occurs in chilling-sensitive plants and the reaction depends on electron flow from PSII to PSI.
caption: Cyanobacteria photosystem II, dimer, PDB 2AXT
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